Cholera is a very old disease believed to have been first described in ancient Greece. Since that time the illness has periodic outbreaks but has steadily declined in its prevalence. The reduction in cases of Cholera is mainly due to the development of modern plumbing and sanitation. For developed countries, cholera is extremely rare. For instance, the last known cases to originate in England were in 1893. All other cases were contracted abroad and imported to the country. This rare prevalence exists in all developed counties and the trend of reduction continues.
In developing countries, Cholera persists in being a dangerous public health issue. According to the World Health Organization (WHO), (2013), “There are an estimated 3–5 million cholera cases and 100 000–120 000 deaths due to cholera every year.” The majority of these cases are located in developing nations with poor sanitation and water resources. The following areas are at the highest risk:
· Africa · Middle East · South and south-east Asia · Rural South America
The threat of cholera is not constant, even in these areas. Typically, outbreaks occur and usually during the summer or when events such as natural disasters or war occur. The danger of Cholera is due to its rapid onset. Cholera if left untreated can kill in hours from the time of infection. Between 1817 and 1824 a cholera pandemic spread from India through Asia and the Middle East and into eastern areas in Africa. The total number of deaths is unknown but thought to be in the millions. The fast rate of infection and morbidity can be seen in the fact that each time there is a pandemic millions of people die. In India, between 1817 and 1860 there were three pandemics which killed approximately 15 million people. This ability to spread quickly and a fast rate of morbidity makes large outbreaks very dangerous because it is difficult to mobilize public health services quickly enough to stop many people from dying.
Vibrio cholera is also known as V. cholerae is the bacteria that causes Cholera. The bacteria exists and thrives in many different mediums but typically it is transmitted via water or food produced with contaminated water. Cholera infects the human host and begins growing and reproducing in the small intestine. The bacteria secretes cholera toxin, which is a protein that that results in diarrhea, severe vomiting, nausea, dehydration, and muscle cramps. Left untreated, the bacteria will kill the host typically through dehydration. The segment of the population most susceptible to infection and death are children and elderly persons.
The transmission and spread of cholera is typically through water but can occur with food that has been contaminated by infected water. The bacteria can be passed from person to person but this is not typical because it requires prolonged contact with body fluids such as blood or urine. The most common form of transmission occurs when the bacteria is passed out of the body through feces which are then introduced into a water source. The bacteria contaminates a source of drinking water which quickly allows the virus to spread through a population. This makes poor water management and sanitation the largest causative agents of Cholera.
Clinical Aspects of Disease
There are several variations of the Cholera virus but only two strains are known to cause outbreaks. The two strains include V. cholerae, O1, and O139 (Howard-Jones, 1984). The O1 strain is the cause of most outbreaks of cholera throughout the world. The O139 strain has caused outbreaks but its prevalence is much lower.
The diagnosis and treatment for Cholera has remained the same for decades The Cholera bacteria is isolated and identified by taking a stool sample. A culture is formed using the sample and the bacteria are then identified by clinicians (Howard-Jones, 1984). There are rapid test kits that public health officials use in epidemic settings but these tests are not as accurate as a stool sample (Howard-Jones, 1984).
The treatment for Cholera includes replenishment of fluids and electrolytes to stop dehydration and Oral Rehydration Salts (ORS) which is a packet containing salts, glucose, and minerals that help the body hydrate. Antibiotics are used to kill the bacteria. There is a vaccine that is available but this is only 85% effective.
Incidence and prevalence rates of Cholera are extremely important to the epidemiology aspects of the disease. While both concepts are similar they represent two different statistical measures with regard to studying the disease. The incidence rate is dependent on the number of new cases during a specific time period. In contrast, prevalence depends on two factors: the number of people who have been ill during previous incidences and the duration of the illness. Those diseases that have a long duration will have a larger prevalence than the incidence rate. Oppositely, diseases with a short duration will have a low prevalence rate (Trident University, 2007). This is extremely important to the study of Cholera because it can determine if an outbreak is contained or if it is becoming a pandemic. The statistical relationship between prevalence and incidence is roughly measured in the ratio: Prevalence = Incidence x Duration
This ratio is not exact and there are a number of other factors which can affect this measure. Some of these factors include; seasonality, broad variability in duration, the susceptibility of other diseases causing death. Cholera is sensitive to seasonality such as being more prevalent in summer but typically does not allow enough time to make the person susceptible to other diseases which cause death. This factor, therefore, does not shorten the duration and does not affect the prevalence rate.
Although both rates affect one another, separately these rates serve different purposes. Prevalence is serving the purpose of determining public health care needs resulting from the burden of chronic disease. In this way, prevalence can be used to monitor the needs of public healthcare. Incidence rates are primarily used for measuring disease risk. The increased incidence will show that the disease is increasing and this can be used to track the disease and to study its causes (Trident University, 2007).
The standard epidemiology model for tracking Cholera is known as SIR or Susceptible, Infectious, and Recovered. The SIR model is a simple and commonly used model for tracking and predicting the spread of Cholera and other infectious diseases including measles, mumps, and rubella. The SIR model is used to show how a communicable disease is spread through the application of the variable of time (t) to the three aspects of SIR. I.E., S(t), I(t), and R(t). The variable of time shows how the disease is progressing and ending. These factors can then be used to plot the spread and the possible end of the disease (Tassier, 2005).
Sample SRI Model
The SIR model works in a simplistic manner by the number of susceptible individuals falling as more of the population becomes infected. The infectious rate then increases as will the recovery rates. This relation of rates over time can be shown in charts which then show a visual progression of the disease.
The SIR model is a simple model but does have drawbacks in that it does not always show specific rates accurately. As individuals die they are removed from the model and this affects all numbers within the model. Using this model, epidemiologists must consider a variety of other factors which can interfere with accuracy of the model.
Because much is known about the spread of Cholera, Epidemiologists have been able to create accurate SIR models known as Aquatic Models (Codeco, 2001). The aquatic model can be used to predict the rate at which a susceptible population becomes infected and how the number of infected increases and decreases over time in relation to the amount of time using contaminated water supply (Codeco, 2001).
In the model shown here the fitted data is the time using the water supply in relation to the number of infected individuals. One can see the utility in this model because it allows the public health official to predict the rate of infection and what level of outbreak is occurring. This is a significant predictive ability because it can determine the resources needed and whether the population is facing an epidemic or a small outbreak.
The Cholera Problem
Cholera is a poor person’s disease. Because poverty conditions create poor sanitation and water management practices, Cholera can still reach epidemic proportions in areas of the world that are underdeveloped. Each year there are between 3 and 5 million cholera cases which results in approximately 120 000 deaths (WHO, 2012). More than 80% of cases could be treated and cured using just oral rehydration salts (WHO, 2012). The lack of public health services and availability of these salts results in deaths for many children and elderly individuals because they are most impacted by the illness. According to the WHO, (2013),
Cholera remains a global threat to public health and a key indicator of lack of social development. Recently, the re-emergence of cholera has been noted in parallel with the ever-increasing size of vulnerable populations living in unsanitary conditions.
Public Health Significance
While outbreaks in developed nations continue to decline, the prevalence in underdeveloped nations has seen a reemergence and increase in the disease. In 2011 WHO reported 589,854 cases from 58 countries (WHO, 2012). The disease continues to rise mainly due to overcrowding and lack of infrastructure in underdeveloped nations. While the known cases are documented the number of total cases remains unknown. Due to the lack of adequate surveillance and reporting in many nations, the number of cholera cases is believed to be much larger than what is known.
The largest risk factors for contracting and spreading Cholera include underdeveloped areas with poor water management and sanitation. These areas become an even higher risk during heavy rains and flooding because these factors increase the risk of contaminating rivers and drinking water supplies (WHO, 2012). In rural villages and remote locations, the risk of a cholera outbreak is high because these areas have no sanitation systems which allow human waste to mix with drinking and bathing water (WHO, 2012). This makes individuals living in poverty and rural areas most at risk.
Costs to Society
The cost of Cholera is often overlooked by individuals in the developed world. When a Cholera outbreak occurs often the trading partners of the nation will halt food trade and travel will also suffer. This has a negative impact on the economies of these nations further disrupting economic growth and the ability to deal with future Cholera outbreaks. This occurred in Peru in 1991. An outbreak stopped tourism and food trade and the country lost $770 million (WHO, 2013). Typically, outbreaks are small and do not warrant this level of sanctions. But as a result of panic, many nations carry a financial and social burden of being associated with the disease and this further impedes their growth.
By supplying these nations with inexpensive Oral Rehydration Salts billions of dollars in lost trade could be avoided each year. The long term benefit of providing these salt cures and even vaccines would reduce the financial losses and allow these nations to build better water and sanitation infrastructure. The cost per ORS is $.50 per treatment course (Every woman Every Child, 2013).
Currently, the proven control strategy for outbreaks is based on reducing deaths by supplying clean water to outbreak zones (WHO, 2012). This has the added impact of limiting the spread of the disease as well as reducing the number of people needing treatment. The provision of water is the largest barrier to dealing with outbreaks. The supply is often limited by inaccessibility and other factors. Another challenge is creating proper sanitation. In disaster areas, Cholera can be spread quickly due to damaged infrastructure (WHO, 2012). Another preventative measure is health education for improved sanitation and safe food handling practices in communities (WHO, 2012). Education is helpful but it is often limited by the infrastructure in communities.
Cholera remains a global threat and prevention strategies seem to hold the best solutions. Vaccination is a possibility but given the problem of super germs that have occurred with other forms of the disease, this may create a larger long term issue. By improving infrastructure and providing inexpensive treatments the nation’s highest at risk can avoid long term costs associated with outbreaks. This will allow these nations the ability to grow economically and build better water management systems. The short term cost for developed nations to provide inexpensive treatment would reduce the need for large expensive interventions during pandemics.
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Every woman Every Child. (2013). Oral rehydration salts (ors) — product profile. Retrieved from http://www.everywomaneverychild.org/component/content/article/1-about/306- oral-rehydration-salts-ors — product-profile-
Howard-Jones, N (1984). Robert Koch and the cholera vibrio: a centenary. BMJ 288 (6414): 379–81.
Trident University. (2007). Incidence and prevalence rates. Retrieved from http://graduate.tuiu.edu/DHS652Sum08/Incidence & Prevalence.htm
Tassier, T. (2005, September 15). Sir model of epidemics. Retrieved from http://www.fordham.edu/images/Undergraduate/economics/faculty/SIR.pdf
WHO. (2012, July). Cholera. Retrieved from http://www.who.int/mediacentre/factsheets/fs107/en/
World Health Organization. (2013). Global epidemics and impact of cholera. Retrieved from http://www.who.int/topics/cholera/impact/en/